Optical stereoscopic viewing systems have been known since practically the advent of photography. The major obstacle encountered in prior systems which has, heretofore, limited their use, has been the inability to confine the sight of each of the observer's eyes to a respective one of a pair of right and left stereoscopic images, while permitting these images to fuse into a single stereoscopic image to the observer.
Attempts have been made to superimpose stereoscopic images onto a single polarizing screen. In this application, the pair of right and left images are polarized and projected onto a special screen that does not lose the polarization of the images which are superimposed on each other. When viewed through polarizing glasses, the illusion of a stereoscopic image is achieved. This system requires the use of elaborate photographic equipment, particularly a specialized polarizing projection system and screen and is not adaptable for electronic transmission, e.g., cannot be transmitted and viewed with television sets.
Some attempts have been made to achieve stereoscopic images with television transmission by use of color filters to view color encoded right and left stereoscopic images which are broadcast and viewed with conventional television equipment. The difficulty with this system is that it compromises both the stereoscopic illusion and the color quality of the images. Furthermore, color discriminate stereoscopic transmission requires the use of encoded filter lenses which if not available or not used results in off color, hazed-edge images. Preferably, a successful system should permit the viewer to see two-dimensional images without compromise of the image quality when the eyepieces, i.e., lenses or filters, are not worn.
The employment of solid prisms and polarizing filters housed in an eyeglass format is disclosed by Karl Schenk in German Patent No. 1,161,128. Other inventors disclosed various uses of solid prisms to refract one or both images at the observer's eye or eyes to achieve stereoscopy. None of the inventions however, accommodate the need, in one pair of glasses, to vary diopter power of the refraction means depending upon the varying distance from the observer to the image source.